A Union flag flies next to the flag of the European Union in London, Britain, November 4, 2016. REUTERS/Toby Melville

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PARIS (Reuters) - France and Ireland on Thursday vented their frustration at the British government's slowness in outlining its plan to leave the European Union saying that they wanted some clarity in the next few weeks.

British Prime Minister Theresa May has promised to trigger Article 50 which would enable the formal divorce talks with the European Union by the end of March, but has so far been tight-lipped about what Britain is seeking to achieve in the two-years of talks which will then follow.

EU officials have also said they would not begin negotiations with Britain until the formal notification is served.

However, contradictory statements from British government ministers on what Brexit could mean have angered EU members.

"The European Union is ready to negotiate. We're in the starting blocks, but we need to start off on a clear basis. If the basis is clear then negotiations will go well," French Foreign Minister Jean-Marc Ayrault told a news conference alongside Irish counterpart Charles Flanagan.

Britain is among the biggest trade partners of both countries, and they potentially have much to lose from Brexit.

"What's important is clarity. You can't pick and choose what you want ... there hasn't been sufficient clarity," Ayrault said, adding that the EU remained fully united in not negotiating on anything before Article 50 was triggered.

"It's now over five months since that (Brexit) decision was taken by the British people and I believe it's important that we move towards clarity and know precisely what the British plan is and it's important that over the next few weeks we see clarity," Flanagan said.